The broad aim of the proposed work is to investigate the physiological control of reproduction in aged male mice. During the previous year attention was focused on identifying and quantifying the steroids elaborated by in vitro perfused testes from 6 months old and 24 months old sexually inactive and active animals. Striking age related decreases in testicular steroid production have been established. We now plan to exploit these findings to determine their significance in the negative feedback control of LH secretion in the aged male. In addition studies will be undertaken to assess the responsiveness of the anterior pituitary gland to gonadotropin releasing hormone and establish the pattern of pituitary LH, FSH and prolactin secretion in aged but robust sexually active and inactive males.